HLA-B27 represents a family of closely related antigens. Six alleles which differ in a limited number of nucleotide substitutions have been described (B*2701--B*2706). These changes are clustered in alpha 1 and alpha 2 domains. Polymerase chain reaction strategies were designed to amplify specific regions of class I exons 2 and 3. Amplified sequences were tested with eight sequence-specific oligonucleotides to distinguish all B27 subtypes. We also subtyped B27 in 50 healthy Spanish individuals using this procedure. The B*2705 subtype is over-represented in our population (96%). The remaining 4% carried the B*2702 allele. This finding is in agreement with the frequencies described by other techniques (cytotoxic T lymphocytes and isoelectric-focusing) for Caucasian populations. Class I oligotyping is a poorly developed field with significant potential applications. This procedure of genotyping B27 alleles is a reliable method which can be used in transplantation and B27-associated disease studies.